Study of HCl and secco defect etching for characterization of thick sSOI

Abstract

In order to continue improving strained silicon-on-insulator (sSOI) crystal quality, high-resolution defect monitoring needs to be developed and implemented for further defects reduction. The study presented in this paper evaluates and compares two techniques for revealing crystal defects in sSOI wafers produced by the Smart-Cut Technology. Two different etching techniques, based on the use of gaseous HCl in an epitaxy reactor or of a diluted Secco wet etching solution, were compared on their ability to delineate various defects. Both techniques should provide the required defects density resolution for analysis of thin and thick strained silicon layers. For the sake of analysis and discussion, samples with a high defects density were chosen in order to simplify the quantitative comparison (within the resolution of optical microscopy). We have observed a difference in etching selectivity between the two techniques. After a statistical comparison of defects delineated by the two techniques (in terms of threading dislocations, areal densities, and planar defect linear densities), we have demonstrated complementarities rather than a direct correlation between the HCl and Secco etch. The HCl etch seems quite suitable for revealing threading dislocations through etch pits and shows a higher sensitivity for pit delineation compared to Secco (difference corresponding to a factor of 10 in defects density). Meanwhile, the Secco chemical etching appears more appropriate to highlight the planar defects (linear density between 600 and 1000 cm-1). Moreover, a minimum etched thickness for sSOI defect revelation has been determined for both techniques (between 26 and 36 nm for HCl and between 20 and 30 nm for Secco for a 600 Å thick starting layer). Because the Secco etch is particularly sensitive for the delineation of various types of defects (isolated etch pits and planar defects), it is now used by us as a quality control method for SOI and sSOI. Thanks to it sSOI process improvements are tracked and current and next generations of this product evaluated. © 2007 The Electrochemical Society.